Insecticide dispenser with a PTC heater

ABSTRACT

An insecticide dispenser capable of initiating the volatilization of a charge of insecticide to fumigate a room. The dispenser includes a container for the insecticide that is disposed upon a PTC heater. One side of the power supply necessary to initiate the chemical reaction passes directly through the cannister to the PTC heater. The other side of the power supply is connected through a support upon which the PTC heater rests. In the preferred embodiment, an electrical cut-off device is included in the circuit which will turn off the power when a predetermined temperature is attained which will be indicative of the initiation of the self-sustaining chemical reaction that causes the dispensing of the insecticide into the room.

FIELD OF THE INVENTION

The present invention relates to electrically heated insecticidedispensers for rooms and particularly to those which are adapted todisperse a charge of insecticide from a container which is to be usedonly once and in which, preferably, the insecticide dispenser can shutitself off automatically when the charge has been dispensed.

SUMMARY OF THE PRIOR ART

Insecticide dispensers are well known to the art and devices havepreviously been introduced which are adapted to dispense insecticidesinto a room when a container is heated. For example, the U.S. Pat. No.4,391,781 to van Lit, discloses a resistance heating device that can beutilized with a strip of paper that has been impregnated with aninsecticide. The paper strip is urged against the resistance heater sothat when the current is turned on, it will dispense the insecticidethat is held on the paper. The paper is held against the resistanceheating element by a clamp arm that presses the mat against the surface.A depressible lever engages the clamp arm and moves it away from theheating surface thereby releasing the paper strip to facilitate itsreplacement. In the van Lit patent, however, no disclosure is made of acontainer of insecticide and the limiting of the dispensing iscontrolled by the amount of vaporizable material that is held within thepaper. No disclosure is made in the van Lit patent of making thecontainer that holds the vaporizable material part of the electricalcircuit that heats it.

Since the present invention relates to dispensers for insecticides thatutilize cannisters which are to be used only once, it is necessary toturn off the resistance heating element when the vaporizable material isfully dispersed into the room. The usual approach for dispensing suchvaporizable material is to initiate the vaporization and then quicklyleave the room where the dispenser has been placed. The room is notreentered until quite a while later, when the vapor has settled and isnot toxic to the person who is doing the fumigation. When using PTCheaters that only attain a predetermined temperature, the possibilitythat the dispenser could overheat and cause a fire is markedly reduced.Thus, while the van Lit patent may be appropriate for dispensing certainsmall quantities of volatilizable material, I have found that it isinappropriate for large scale fumigation of entire rooms.

The U.S. Pat. No. 4,202,472 to Lin, discloses the use of a device forbagging trash and simultaneously dispensing insecticides or, repellents.The insecticide or repellent is slowly dispensed into the trash toprevent the breeding of micro-organisms. The device does not involve theuse of electrical heating for the container and dispenser and thus isnot adaptable for use for fumigating a room. The U.S. Pat. No. 4,316,279to Beacham, discloses a combined container and dispenser for dispensinga volatile product such as an air freshener or insecticide. Theinvention involves a continuous, low rate dispensing of the volatileproduct in an ambient atmosphere and is especially not related to thesudden volatilization of large quantities of insecticides such as arecontemplated in the present invention. The invention of Beacham isdesigned to be unobtrusively stuck or hung to a hidden surface so thatit is not normally observable by persons nearby whereby the vaporizablematerial will slowly disperse into the room where it is disposed.

Automated aerosol mist dispensers are disclosed in U.S. Pat. No.3,974,941 to Mettler. Patentee discloses a device for injecting shortbursts of an atomized liquid such as air fresheners, medicines orinsecticides at desired intervals from a spray nozzle in communicationwith a conventional aerosol can that contains a fluid under pressure.With Mettler's invention, an automated aerosol mist dispenser isdisclosed that affords a secure interconnection between the pressurizedcan of fluid and the control valve mechanism and which is safe againstundue leakage, even at relatively high temperatures owing to theprovision of a balancing piston feature. No concept, however, isdisclosed by Mettler for dispensing a large volume of insecticide into aroom in a single charge through the use of a PTC resistance heatingelement.

U.S. Pat. Nos. 3,151,785, to Scarpa, and 3,466,789, to Kare, involve theuse of liquid insecticide dispensers in which the rate of liquid that isbeing dispensed is controlled though slow dripping of the liquid andsubsequent atmospheric volatilization. While Kare may disclose a singledose dispenser for the insecticide, no disclosure is made ofelectrically heating the dispenser to volatilize its contents.

SUMMARY OF THE INVENTION

According to the present invention, I have discovered an insecticidedispenser that can be electrically heated with a PTC heater to dispensethe insecticide. In the preferred embodiment, the dispenser of thepresent invention will be able to shut itself off automatically when thevaporization has commenced, or at least before the vaporization has beencompleted. The dispenser includes a housing with an electrical contactdisposed on the sidewall that is arranged to contact the sidewall of anelectrically conductive insecticide container. The container is disposedon the PTC heater (as will be described later) which is connected to apower source and is made part of the circuit with the container andproduce heat. Heating the container will initiate a self-sustaining,exothermic chemical reaction in the mass of insecticide and carrier thatis in the container which will volatilize the insecticide and disperseit into the room.

When the insecticide is volatilized, the container of the presentinvention cannot be used again, thereby preventing the possibility ofinjury to the user through subsequent uses or refilling it withmaterials that are not designed to be used with the dispenser. Moreover,the utilization of the dispenser of the present invention involves afumigator setting up the device and then turning on the power tocommence the volatilization of the insecticide. When the heating hascommenced, the fumigator should promptly leave the room in which theaction has been initiated and close the door, thereby containing theinsecticide within the room and allowing it to do its work. The doorshould not be opened for a significant amount of time so as to preventpoisoning the fumigator. Since it is frequently undesirable to continueheating the container that holds the insecticide for all of the time thefumigator is out of the room because of the possibility of overheatingor fire, in a further preferred embodiment of the present invention, thedispenser is designed to turn itself off by breaking the electricalcircuit.

PTC heaters have been in use for many years. I have found that suchheaters offer several operating advantages over conventional resistanceheating elements in the heating of containers of insecticides. Theygenerally are flat and made from doped barium titinate ceramics whichhave a sharp positive temperature coefficient of resistance. The PTCceramics are designed such that below a critical temperature, theresistance of the ceramic remains at low value and is essentiallycontant. When a particular temperature is reached, a crystalline phasechange takes place in the creamic and this abrupt change in crystalstructure is accompanied by a sharp increase in the resistance at thecrystalline grain boundaries. The result of this crystalline change isan increase in the heater resistance of several orders of magnitude overa very small temperature change. A barium titinate heater with a roomtemperature of resistance of 3.0 ohms will increase to 1000 ohms or moreduring the crystalline phase change. The temperature at which thecrystalline phase change takes place can be adjusted in the PTCmanufacturing process through the use of appropriate chemical additivesand can be varied between 60 and 180 degrees centigrade, therebyproviding a range of temperatures to suit various combinations ofinsecticides and carriers.

When used as a heater and energized with a suitable voltage by applyingcurrent to the opposite side of it, the PTC ceramic rapidly heats up toa predetermined operating temperature and then "locks in" at thistemperature. This rapid warm up is due to the initial low resistance ofthe PTC ceramic heater which results in an internal high power input ofthe heater. The "lock in" is due to the abrupt increase in resistancewhich causes generated power to be reduced until it equals thedissipated power. At this point, a thermal equilibrium is achieved andthe PTC heater self regulates itself at that temperature until it isturned off.

When the container of insecticide is placed directly upon the face ofthe PTC heater, an electrical circuit will be formed when using thedispenser of the present invention. Placement will cause the PTC heaterto begin to heat. The circuit is between a connection disposed in thehousing of the dispenser, through the insecticide container and then tothe PTC heater. The heat from the PTC heater is transmitted to thecontainer that holds the insecticide. Preferably the circuit can bebroken easily by placing a movable insulator between the connection inthe housing and the container. As an example of such an insulator, aplastic cap is placed on the top of the container and a cavity is beformed in it which will allow the electrical contact to enter the cavityand engage the container. When the circuit is to be broken, the cap (andthe entire container, also, if desired) can be twisted to place the capbetween the container and the connection, thereby preventing the flow ofcurrent. In another preferred embodiment, a mass of eutectic material isplaced over an aperture in the bottom of the container. An electricallyinert pin is urged against the bottom of the mass of eutectic materialby a spring member that electrically connects the lower side of the PTCheater to the other side of the power supply. When the eutectic softens,the pin member will move towards the container and break the circuitautomatically. Dispensing of the insecticide will continue because ofthe self-sustaining chemical reaction that was initiated by the PTCheater, even though the circuit has been broken.

DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of thisinvention, reference should be made to the following detaileddescription taking in conjunction with the accompanyng drawings whereinlike reference characters refer to corresponding parts throughout theseveral views of the preferred embodiments of the invention and wherein;

FIG. 1 is an elevational view, partly in cross-section of an insecticidedispenser prior to initial heating with the circuit connected tovolatilize the insecticide and

FIG. 2 is a similar view of the same device arranged in a way so thatthe circuit is broken and the insecticide is dispensed.

FIG. 3 is an elevational cross-sectional view of another embodiment ofthe present invention illustrating a cut-off device suitable for turningoff the current to the PTC heater, automatically, before the insecticidecontained in the device is completely volatilized.

FIG. 4 shows a similar view of the equipment after the current to thePTC heater has been shut off when the insecticide has been volatilizedinto the room which is being fumigated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 illustrates an embodiment of theinvention in which an electrically conductive insecticide container 1 issnugly fitted in a housing 3. A PTC heater 5 is disposed upon a support7 which is formed on the inside of the side wall 3a of the housing 3. Anelectrical contact member 9 is arranged on the side wall 3a of thehousing 3 and is arranged to urge against the container 1 so as to makethe container 1, one side of an electrical circuit. The electricalcontact member preferably includes a movable, spring-loaded ball 9awhich presents its face from an aperture within the contact 9. A spring9b is connected to the power supply through a lead-in wire 11.

The lead-in wire 11 extends to the contact ball 9a through the side wall3a and the base of the housing 3 and runs external thereof to a plug 15.The lead-in wire 11 branches to electrically connect with a conductivesupport 17 upon which the PTC heater 5 rests so as to provide current tothe lower side. As shown in FIG. 1 of the drawing, the ball 9a engagesthe electrical conductive container 1 which, in turn, rests upon theupper side of the PTC heater 5. With this arrangement, the circuit isformed between the two sides of the lead-in wire 11 with one side beingestablished between the support 17 and the other with the bottom of thecontainer 1. A plastic cap 12 with a spout 13 (which allows theinsecticide vapors to escape during operation of the dispenser) isdisposed upon the top of container 1. The plastic cap 12 also serves asa circuit breaker, as will be discussed later. Cap 12 is permanentlyseated upon the top of the container 1 by means of flange 1a which fitsinto an groove or recess 12a which is located near the top of the innersurface of cap 12.

THe mass of insecticide 2 that is held within the container 1 includes aconventional insecticide dispersed in a well-known chemical carrier suchas oxygenated wax, which upon the application of heat, will produce aself-sustaining chemical reaction that will volatilize the insecticideand dispense it into the room. In the preferred embodiment, the carrieris such that it will chemically react in an exothermic chemical reactionupon the application of heat from the PTC heater 5. The chemicalreaction, as is well know, is self-sustaining upon initiation and theheat from the exothermic reaction will vaporize the insecticide todisperse it into the room. When the PTC heater 5 reaches itspredetermined anomaly temperature due to the heat of the reaction, itwill maintain that temperature and not overheat.

At an appropriate time after the chemical reaction in the insecticidehas commenced or after the volatilization is completed, the cap 12 isturned on its axis, together with container 1, by rotating the handle 14which will change the location of cavity 15 (comparing FIG. 1 and FIG.2) relative to ball 9a. Since ball 9a is spring-loaded, it will enterinto the cavity 15 when the cap 12 is turned. Because ball 9a no longerengages container 1 when The handle 14 is turned, the electrical circuitformed on the opposite sides of the PTC heater 5 will be broken.

After the vaporization of the insecticide has been completed, thefumigator can reenter the room, using appropriate precautionary measuresto avoid inhalation of the insecticide, and disconnect the plug 15, oras described above, turn the handle 14 and the heating provided by PTCheater 5 will be terminated. Container 1 can be withdrawn by thefumigator by pulling handle 14 which will remove it from the housing 3.

Another preferred embodiment of the present invention is shown in FIGS.3 and 4 in which the container 61 of insecticide 62 is disposed within ahousing 63 and means are provided to automatically discontinue theheating after the vaporization of the insecticide has commenced andpreferably before it is completed.

The electrically conductive container 61 holding a charge of insecticide62, as described previously, is disposed within a insecticide dispenser63 having a side wall 63a and a base 63b. The container 61 rests uponthe PTC heater 65 as described previously. The PTC heater 65 is disposedupon an electrically conductive shelf 66 which carries current to oneside of the heater, as will be described later. A retainer 67 isdisposed on the side wall 63a of the dispenser and holds the top of thePTC heater 65 firmly in place.

Current is carried to one side of the PTC heater 65 through theelectrically conductive container 61 which is in contact with aspring-loaded conductive button 66 that is fitted into the side wall 63aof the dispenser 63. The button 66 extends inwardly from the side wall63a of the dispenser 63 to slidably engage the side wall of thecontainer 61. When the plug 67 is placed in a standard wall receptacle,current will pass through line 68 to contact button 66. The lead-in wire68 splits at location 70 and one side extends through the side wall 63awhile the other side is attached to electrical contact 71. Electricalcontact 71 is rigidly disposed on the side wall 63a of the dispenser 63.Rigid disposition is obtained through the use of a support 72 thatextends inwardly from the side wall 64. An electrical connection is madeto the under side of the PTC heater 65 through spring-loaded (73a)bracket 72 that is also rigidly attached to the side wall 63a of thedispenser 63. A connecting wire 79 connects bracket 73 to electricallyconductive shelf 66. Spring-loaded bracket 73 can pivot about support 74to open or close the circuit at location 75. The spring-loaded bracket73 is urged toward the closed position at location 75 by means of aplastic pin 76 which urges against an opening in the bottom wall of thecontainer 61. That opening is covered by a slug of eutectic 78 that isattached to it. The slug of eutectic, 60/40 solder for example, softensat a relatively low temperature. Other eutectics can also be used whichwill precisely soften at a desired temperature and will be compatiblewith the exact temperature that an electrical cutoff is desired. The pin76 is slidably received through the center of the PTC heater 65 and heldwithin a sleeve 77, preferably made of a high melting plastic such as isused to form the pin 76. It is possible to use other electrically inertmaterials such as asbestos which will not degrade upon heating at therelatively low temperatures that are established in the PTC heater 65.

When the chemical reaction in the charge of insecticide 62 is initiated,the sealing slug of eutectic 78 begins to soften due to the exothermicnature of the chemical reaction. Even a slight softening will cause theplastic pin 76 to move upwardly and disengage the electrical connectionat location 75. The disengagement of the electrical connection atlocation 75 is best shown in FIG. 4. Current cannot be conveyed to thelower side of the PTC heater 65 by means of the connecting wire 82 whenthe connection at location 75 is broken. The eutectic slug 78 does notmelt completely, but rather softens to allow the pin 76 to enter thecontainer through the aperture 80 located in its base. Only a sightmovement of the pin 76 will produce a breaking of the circuit atlocation 75, thereby discontinuing the current but allowing thevolatilization of the mass of insecticide to continue to completion.Replacement of a fresh can of insecticide with a new eutectic slug thatis flush with the bottom of the container will automatically reset theelectrical connection at location 75 which will enable the fumigator tocontinue to use the insecticide dispenser.

It is apparent that modifications and changes can be made within thespirit and scope of the present invention but it is my intention only tobe limited by the appended claims.

As my invention I claim:
 1. An insecticide dispenser including ahousing, a PTC heater disposed therein, said PTC heater having an upperside and a lower side and an electrically conductive container for aninsecticide disposed on the upper side of said PTC heater; andone sideof a power supply means being connected to said conductive containerand, in turn, to the upper side of said PTC heater; and an other side ofthe power supply being connected to the lower side of said PTC heater,whereby when said electrically conductive container is disposed on saidPTC heater, a circuit will be formed on both sides of said PTC heaterthrough said container, and further whereby heat is provided to initiatean exothermic self-sustaining chemical reaction in said container tovolatilize insecticide therein.
 2. The insecticide dispenser accordingto claim 1 wherein said one side of a power supply is connected to saidcontainer through a spring means disposed on a side wall of saidhousing, said spring means engaging said container whereby to form anelectrical connection between said spring means and said container. 3.The insecticide dispenser according to claim 2 further includingelectrical cut-off means arranged to stop the flow of current to oneside of said PTC heater.
 4. The insecticide dispenser according to claim1 wherein said container has an electrically inert cap with a ventdisposed on the top thereof and further including cavity means on a sideof said cap to allow said spring means to enter said cap and engage aside wall of said container.
 5. The insecticide dispenser according toclaim 4 wherein said cap is permanently secured to said containerwhereby contents of said container cannot be spilled or otheringredients conveniently added.
 6. The insecticide dispenser accordingto claims 2 or 3 further including a thermal shut-off, said thermalshut-off including an aperture in a bottom of said container and slug ofeutectic covering said aperture; anda pin having two ends, one end ofwhich engages an outside of said aperture; and resilient means engagingthe other end of said pin, whereby upon softening of said eutectic, saidresilient means will force said pin into said aperture, wherebyelectrical current between said resilient means and said PTC Heater willbe broken.
 7. The insecticide dispenser according to claim 6 wherein thepin is an electrical insulator and extends through an aperture in saidPTC heater to urge against said container.
 8. The insecticide dispenseraccording to claim 7 wherein said PTC heater rests upon an electricallyconductive shelf and electrical connection between said resilient meansand said PTC heater is through said shelf.
 9. The insecticide dispenseraccording to claim 8 further including an electrically inert sleevedisposed in the aperture in said PTC heater.